1. Field of the Invention
The present invention relates to multi-line wireless telephone systems and, in particular, to data transmission in a time-division multiplexed (TDM) wireless telephone system.
2. Description of the Related Art
The use of telephones and telephone systems, including wireless telephone systems, is widespread. In wireless telephone systems, a cordless or wireless telephone handset unit communicates via either analog or digital radio signals with a base unit, which is typically connected via a standard telephone line to an external telephone network. In this manner, a user may employ the wireless handset to engage in a telephone call with another user through the base unit and the telephone network.
Multi-line wireless telephone systems are in use in various situations, such as businesses with many telephone users. Such systems employ a handset that communicates with up to N handsets simultaneously, typically with digital communications schemes, such as a spread-spectrum, time division multiple access (TDMA). In a TDMA system, a single RF channel is used, and each handset transmits and receives audio data packets as well as non-audio data packets during dedicated time slices or slots within an overall TDMA cycle or epoch. It is desirable to provide various features, such as private branch exchange (PBX) features and capabilities, in a multi-line wireless telephone system. It is also desirable to transmit or retrieve non-audio data over the RF channel. For example, a handset may wish to retrieve certain stored data, such as voice mail or caller ID data, which is stored in the base unit or in a device coupled to the base unit.
European Patent Application No. 0 399 611, filed 22, May 1990, describes a communications system for data transmission over a time division duplex frequency channel, in which TDMA is used for forward and reverse transmissions between a primary and secondary station.